'Kabhi Haan Kabhi Naa' is a poignant coming-of-age drama that primarily revolves Sunil (Shahrukh Khan) an extroverted and fun-loving young man, whom everyone loves, except his own father Vinayak. Sunil and his friends start a band and Anna, his childhood friend, who returns to their hometown after many years, subsequently joined the band, much to the excitement of all.
Sunil is secretly, head over heels in love with Anna, and the only other person who is aware of this fact is his sister. As Anna joins the group, they embark upon the active search for opportunities to make it big in the music world. Chris, another band member and Sunil's best friend, is Sunil's antithesis in nearly everything; Chris is a studious person and son of an affluent couple.
Anna's father decides to get her married to Chris. Now, Sunil tries to change his image to win Anna's love, but when he learns that Anna loves Chris too, he is devastated. A jealous Sunil starts creating a rift between the two but eventually gets caught. Anna slaps him and walks away. Gradually, the duo forgive Sunil, but they don't realize why he did this. Sunil's fortune takes a turn once again when Chris's parents refuse the marriage of Chris and Anna, because Anna is from a lower class. Chris has to leave Anna devastated.
Sunil consoles Anna in this period. Now, the tide has seemingly turned in Sunil's favour and Anna's father gives a go to their marriage. Sunil is happy, until he learns that Anna still loves Chris. Sunil decides to re-unite them. The Sullivans too realize their mistake. Chris and Anna's wedding is announced: Sunil gets to be the best man. As Chris and Anna are about to exchange rings, Chris's ring slips out of his hand. Everybody starts searching for it. Whoever gets the ring can claim Anna's hand. So, Sunil gets one more chance. Sunil spots the ring but feigns ignorance. Chris finally "finds" the ring and marries Anna.
Just after the wedding, Sunil is shown packing his bags and leaving his father's home to find his own destiny. Vinayak, who has learnt the background story, makes up with his son, stating that he is proud to be Sunil's father. How will Sunil's future unfold?